Various types of synthetic diamond products are known and commercially available. Typically such products are used industrially for material removal purposes, for example, drilling products such as core bits, mining bits, drilling bits for oil and gas, saw products, cutting tools, grinding wheels, and products such as wire-drawing and extruding dies, bearing surfaces, dressers, lead bonding tools and abrasives.
These synthetic diamond materials may vary somewhat in their character, one being an unleached polycrystalline product having a temperature stability of up to about 700-750 degrees C., see U.S. Pat. Nos. 3,745,623 and 3,609,818. This synthetic diamond product itself is usually formed by diamond-to-diamond bonds and is carried on a substrate which may be cemented tungsten carbide, for example. The substrate is usually preformed and contains cobalt, the diamond product being formed and affixed to the substrate at very high temperatures and pressures, usually referred to as the diamond stable region of temperature and pressure, as set forth in prior patents and other literature, and typically above 50 kbar and at a temperature above about 1,200 degrees C.
These products are often referred to as polycrystalline diamond products (PCD) as contrasted to single crystal diamonds. PCD elements offer the advantage that upon fracture, only a relatively small fragment of the PCD element is lost as compared to a single crystal diamond in which fracture takes place along a plane with the possibility of losing a relatively large piece of the diamond.
Unleached PCD elements may be formed with the high temperature and high pressure apparatus as disclosed, for example, in U.S. Pat. No. 2,941,248. PCD products thus far described are available in various sizes and shapes, for example circular, half-circles, quarter round, square, rectangular, half-rounds with a pointed section, and the like. The PCD face or disc, joined to a backing member of tungsten carbide or the like is sometimes mounted, by brazing, on a steel tool body or tungsten carbide slug support. The PCD materials may be as small as several millimeters to as large as 50 millimeters in diameter, see for example U.S. Pat. application Ser. No. 906,169, filed Sept. 11, 1986, and assigned to the same assignee (CHP 6149).
Inclusions such as cobalt, iron or nickel present in unleached PCD elements as residual materials initially used as solvents/catalysts in the synthesis of the PCD tend to reduce the temperature stability of the PCD to well below 1,200 degrees C., for example, to about 750 degrees C.
The fabrication of the larger diameter materials requires rather large and expensive processing equipment capable of generating high pressures and temperatures. The temperatures and pressures are those in the diamond forming region of the phase diagram for carbon, see for example U.S. Pat. No. 4,108,614 and 4,411,672. The length of the substrate or backing is a limitation since the processing equipment must be capable of fabricating a diamond facing on a rather long piece which takes up room in the press. The result is that in at least one instance, the length of the backing, axially to the rear of the PCD face, is rather short and after formation, a longer tungsten carbide member or member of other material is attached to the formed product by any one of several well known procedures, and as described in U.S. Pat. No. 4,200,159, for example.
In one typical use of these products, for example in oil and gas drilling bits and core bits, the usual practice is to form the bit body and thereafter to mount the PCD cutting element in the bit body. The bit body may be steel and the PCD cutter is a slug type cutter which is press fitted into apertures in the bit body. A difficulty with the use of steel bodies is that the body may be subject to erosion by the relatively abrasive flow of the drilling fluid used to clean and cool the bit. Thus, the practice has been to hard face the steel body.
In the case of matrix body bits which offer erosion resistance, the practice has been to mount the slug type PCD cutter by brazing the cutter to the matrix body. One of the problems associated with this procedure, in addition to the increased cost, is the desire to use a relatively high temperature braze material and the need to keep the PCD face cool to prevent thermal damage (above about 750 degrees C.) to the cutter face during the brazing operation. Even so, a large number of bits have been made as described by a variety of bit manufacturers.
Another commercially available form of PCD, sold under the mark GEOSET, is an unbacked leached product, see U.S. Pat. Nos. 4,224,380 and 4,288,248, which has a temperature stability of up to 1,200 degrees C., but which may have a porosity of up to about 15% and may not be as impact resistant as desired in a particular application. The temperature stability of these PCD products offers the advantage that they can be exposed to the relatively high temperatures used during the infiltration procedure used to form the bit body without degradation of the PCD, thus eliminating the need for brazing. In general, temperature stability is also an advantage in the cutting action of the PCD during use. For the purposes of this invention, temperature stability means that the PCD element, regardless of type, is stable to about 1,200 degrees C. without significant deterioration in its properties and will be referred to herein as TSPCD.
Temperature stable PCD elements are known which are not porous and are not leached. A typical such material, available under the trademark SYNDAX-3 is a PCD in which silicon is present in the form of silicon carbide.
Significantly, the TSPCD materials are not commercially available as backed products, as contrasted to the previously described low temperature products. The TSPCD materials are available as unbacked materials in a wide variety of shapes and sizes and they may be cut to form additional shapes by using a laser or other means.
While temperature stability is not required in all uses, there are many applications in which it is required. Further, there are processing steps such as brazing in which the PCD part may be exposed to temperatures above 750 degrees C. In these instances it is necessary to cool the PCD part or to otherwise prevent it from being exposed to the higher temperature. As a result, there are limitations in the processing of such unstable PCD products which tend to limit the use thereof.
TSPCD elements, are available in a limited range of sizes that are generally too small for individual use in many applications. To overcome this problem, TSPCD elements have been formed into a mosaic type of structure in which the individual TSPCD elements are mounted and mechanically affixed in a support structure, e.g., a hot-pressed segment or the like, see U.S. Pat. applications Ser. No. 797,858; 794,569 and 797,445, filed respectively on Nov. 14, 1985, Nov. 4, 1985 and Nov. 13, 1985, and all assigned to the same assignee as this application.
While these mosaic structures have been operated satisfactorily and provide a large PCD cutter having temperature stability, the mosaic elements lack the advantages of the large one piece PCD cutters(up to 50 mm diameter or more) which are not temperature stable but which have been used in oil and gas drill bits and core bits. Even though the bits using the mosaic cutters avoid the necessity of having to braze the mosaic into the matrix of the bit, the mosaic cutters do not function as a large one piece PCD since the individual mechanically mounted TSPCD elements can be broken free of the supporting structure. A mechanical type of mounting also limits the shape and size and contour of the cutter, even though the assembly is temperature stable.
Another problem with known mosaic cutters is that bending stresses tend to cause release of the mechanically mounted TSPCD elements. Moreover, unlike a large integral brazed PCD cutter of the same size in which only small portions of the PCD are fractured off during use, the tendency in the mosaic cutters is to release entire TSPCD elements as the supporting structure around the TSPCD is abraded away and support for the TSPCD is reduced, i.e., the individual TSPCD element is lost rather than losing only a small fragment.
In general there is a need for a TSPCD containing product in which one or more TSPCD elements are firmly anchored or locked into or mounted on a suitable support, which optionally may be mounted to another structure. It is desirable to mount one or more of such TSPCD elements by more than merely a mechanical mounting, and preferably it is desired that the mounting be by a firm chemical bond.
U.S. Pat. No. 3,650,714 of Mar. 21, 1972, issued to Farkas, describes a method for coating natural single crystal diamond particles in the range of 200 to 250 mesh with either titanium or zirconium. The coating is applied from dry powder, the resultant material is then heated in a graphite mold, under vacuum conditions for between 10 to 15 minutes at a temperature in the range of 850 to 900 degrees C. The relatively low temperature of heating to form a carbide at the interface indicates that the titanium or zirconium coating is quite thin. The result is said to be a coated diamond particle in which the coating is about 5% by weight of the resultant product and in which a carbide is formed at the interface, with the outer surface of the coating being non-carbided. The calculated thickness of the coating is about 0.445 of a micron for 200 mesh material and 0.344 of a micron for 250 mesh material. Since subsequent processing in an oxidizing atmosphere would result in the formation of an oxide which is not easily wetted by other materials, the coated natural diamond particles are overcoated with either nickel or copper with a film thickness of between 0.002 and 0.005 of an inch (between 50.8 and 127 microns thick). This outer coating is said to serve as a protective coating to prevent oxidation of the titanium or zirconium or their carbides during subsequent processing under oxidizing conditions. The subsequent processing described is hot or cold pressing and subsequent sintering or infiltration with brazing alloys.
An important difficulty with the above procedure and the resulting product is that the carbide containing coating is quite thin, substantially less than one micron, with the result that under certain types of subsequent processing such as with the use of liquid binders in infiltration, as for example in the formation of an infiltrated matrix for earth boring bits, the liquid binder penetrates the protective coating and the relatively thin carbide containing coating. The problem would be particularly acute with PCD elements since their surface is rather "rocky" and irregular and includes a certain amount of surface porosity. Thin coatings such as described in Farkas would contain substantial imperfections and voids that would permit the liquid infiltrating binder to attack the carbide interface between the PCD and the coating and to separate the coating from the PCD. In addition, the processing of such coated diamonds, whether PCD elements or natural, in an oxidizing atmosphere is not practical since any imperfection or dissolution of the outer nickel or copper coating, for instance by the action of the liquid binder, would result in the oxidation and destruction of the underlying titanium and titanium carbide layer.
Also known in the prior art are products which might be generically referred to as diamond impregnated products. Typically these products are composed of natural or synthetic diamond particles which may be of a variety of mesh sizes. Whereas a large integral PCD element may be between 70% and 97% by volume of diamond material, depending upon the processing, the amount of residual inclusions or porosity, the impregnated products generally have a much lower volume percent of diamond, typically less than 40%. The result is that the impregnated product performs better as an abrasive or cutting element than does the same material without the diamond grit, but the problem is that the small diamond particles are easily lost as the surrounding supporting structure is abraded away. To improve the retention of the diamond grit in the supporting structure it has been proposed to coat the particles of the grit with various metals such as tungsten, tantalum, columbium, niobium or molybdenum, and the like by chemical vapor deposition techniques using a fluidized bed procedure, see for example U.S. Pat. Nos. 3,871,840 and 3,841,852. The products there described are about 25% by volume of diamond grit of particle size from 40 to 100 mesh and represent an improved impregnated product in contrast to an improved large diamond product. The coated diamond grit is formed into various shapes by a hot pressing procedure or by infiltration at an elevated temperature.
Coatings have also been used to form diamond products as contrasted to impregnated products. For example, U.S. Pat. No. 3,879,901 describes the vacuum deposition of a metal such as molybdenum or titanium on diamond materials with subsequent processing at 60 Kbar and between 1,200 and 1,400 degrees C. to form a diamond product. In another instance, see U.S. Pat. No. 4,378,975, an abrasive body with diamond is formed by forming a green body by cold pressing with a nickel based alloy. The green body is then sintered at 950 degrees C. with a diamond volume of between 10% and 40% by volume.
It is also known in the sintering of synthetic diamond to use a thin coating of between 300 and 6,000 Angstroms of a strong carbide former, with a second coating of copper with subsequent processing at 5 Kbar at a temperature of 600 to 700 degrees C. in an inert atmosphere, see U.S. Pat. No. 3,356,473. In U.S. Pat. No. 3,464,804 it is proposed to form a chemically bonded coating of titanium such that a titanium-carbon bond is formed followed by processing at 62,000 atmospheres of pressure.
In general, the coating procedures of the prior art are related to pretreatment of diamond forming materials which are thereafter processed at relatively high temperatures and pressures to form a diamond element or to form a coating on diamond grit used to form an impregnated product in which the volume of diamond is well below about 50% by volume.
The provision of improved methods for the fabrication of large TSPCD products, which are temperature stable in the range of about 1,200 degrees C. and which may be fabricated at lower pressures and temperatures than have been used in the synthesis of diamond products, would have unique advantages. For example, the cost for fabrication equipment is vastly reduced as well as the cost for each of the products. The ability to fabricate various shapes and sizes and thickness, i.e., to be free of the shape and size limitations of high-temperature and high pressure equipment, would also offer advantages from a processing and application point of view.
One of the significant advantages of the present invention is the ability to fabricate a TSPCD product of a particular configuration and in which the TSPCD starting element or elements are firmly anchored in place on a matrix backing. The term "matrix" is used to describe the powder and binder material which is placed around or in contact with the TSPCD element and which is processed in accordance with this disclosure. As will be described, this matrix may, for instance, be formed either with a highly compacted ceramic powder, sometimes referred to as a "matrix carrier", such as might be used as a cutter for an earth boring bit, or with a non-compacted ceramic powder, such as might form the body of an earth boring bit. In either case, the final matrix is formed by infiltration with a molten binder alloy or by solid state sintering.